1. Technical Field
The present invention relates generally to a microwave pulse generator and, more particularly, to a variable frequency microwave pulse generator which includes a pair of electrodes which define a spark gap in order to generate a strong electromagnetic wave pulse, in which the central frequency of the emitted electromagnetic wave and a resultant output waveform can be adjusted.
2. Description of the Related Art
In general, strong electromagnetic wave pulse generators can be divided into a narrowband device and a wideband device depending on the frequency bandwidths. A narrowband electromagnetic wave pulse is typically generated in response to a high voltage being supplied for several tens of nanoseconds, using the movement of an electron beam that causes a high level of kinetic energy. In contrast, a wideband electromagnetic wave pulse is typically generated using spontaneous switching that causes a rise time of less than a nanosecond. The wideband electromagnetic wave pulse is a pulse having a relatively wideband frequency component proportional to a time-dependent variation rate.
Therefore, in a wideband generator, technology for a high-voltage, ultra-fast switch, which generates rapid pulse power, and technology for fabricating an antenna which efficiently radiates a wideband frequency component are very important. An impulse radiating antenna (IRA), a TEM horn antenna and the like are widely used as representative antennas.
Unlike the wideband generator in which the switch and the antenna are separately provided and are detachable, there is a structure in which the switch and the antenna can be directly coupled with each other and designed as a unitary body. Although the directivity of the antenna is limited, this structure is simple and can store electric energy while concurrently performing the functions of generating and radiating a wideband pulse. This structure can also reduce the problem of mismatch between the switch device and the antenna, so it can obtain superior efficiency. Consequently, this structure can radiate a significant intensity of an electric field.
In such a pulse generator in which a switch and an antenna are coupled, a conventional method was proposed in order to generate a varying waveform. In a wideband high-power pulse generator using a dipole antenna, there was proposed a method capable of generating waveforms having a variety of frequency signals by adjusting the length of dipoles which can be separately attached to both ends of the switch. Unlike the switch section which is operated within high pressure gas, the dipole sections are exposed and are vulnerable to dielectric breakdown with the increasing voltage. The damped sine wave characteristics in a high-frequency band occurring at a short length of the dipole change into a wide bandwidth due to the addition of a resonance component corresponding to the length when the length of the dipole is increased. Thus, there is a limit upon generating waveform having frequency-concentrated characteristics in a low frequency band.
In addition, in the conventional structure in which the antenna and the switch are designed as a unitary body, there is a structure capable of adjusting the distance between the electrodes by forming a threaded surface in one surface into which one electrode is inserted. Although the characteristics of the output waveform change in part when the distance between the electrodes is adjusted, the discharge characteristics of the spark gap switch also change. In the structure in which high pressure gas is sealed, the gas must be removed, which is inconvenient.
Also proposed is a structure in which a separate conductor rod is disposed outside the unitary structure and the distance and length of these components are adjusted to achieve variable frequency characteristics. However, the frequency bandwidth that can be varied is very small and the use of this structure is limited.
A related conventional approach includes Korean Patent Application Publication No. 10-2010-0084901 (“SPARK SWITCH GAP MODULE FOR ULTRAWIDE ELECTROMAGNETIC RADIATION,” dated Jul. 28, 2010).